pentose-phosphate shunt, oxidative branch
Definition
Target type: biologicalprocess
The branch of the pentose-phosphate shunt which involves the oxidation of glucose 6-P and produces ribulose 5-P, reduced NADP+ and carbon dioxide (CO2). [ISBN:0198506732, MetaCyc:OXIDATIVEPENT-PWY]
The oxidative branch of the pentose phosphate pathway, also known as the hexose monophosphate shunt, is a crucial metabolic route that diverges from glycolysis. It's primarily responsible for generating NADPH, a reducing agent vital for biosynthesis and detoxification, and pentose sugars like ribose-5-phosphate, a building block for nucleotides and nucleic acids. This branch begins with glucose-6-phosphate, the same starting point as glycolysis.
1. **Glucose-6-phosphate Dehydrogenase (G6PD) Catalyzes the First Step:** G6PD catalyzes the oxidation of glucose-6-phosphate to 6-phosphogluconolactone, using NADP+ as an electron acceptor, generating NADPH. This reaction is irreversible and is considered the rate-limiting step of the oxidative branch.
2. **Lactonase Converts Lactone to Acid:** The 6-phosphogluconolactone is quickly hydrolyzed to 6-phosphogluconate by lactonase.
3. **6-Phosphogluconate Dehydrogenase Produces Ribulose-5-phosphate:** 6-Phosphogluconate dehydrogenase catalyzes the oxidative decarboxylation of 6-phosphogluconate to ribulose-5-phosphate. This reaction generates another NADPH molecule.
4. **Isomerization and Epimerization:** Ribulose-5-phosphate can be isomerized to ribose-5-phosphate by the enzyme ribulose-5-phosphate isomerase. Alternatively, it can be epimerized to xylulose-5-phosphate by ribulose-5-phosphate epimerase.
5. **Transketolase and Transaldolase Interconvert Pentose Sugars:** The oxidative branch culminates in the interconversion of pentose sugars via transketolase and transaldolase. These enzymes facilitate the transfer of two- and three-carbon units between various sugar phosphates, ultimately leading to the production of fructose-6-phosphate and glyceraldehyde-3-phosphate, which can re-enter glycolysis or gluconeogenesis.
The oxidative branch is a tightly regulated pathway, with G6PD activity being influenced by the cellular NADPH/NADP+ ratio and other factors. It's essential for various cellular processes, including:
* **Red Blood Cell Integrity:** NADPH produced by the oxidative branch is critical for maintaining the integrity of red blood cells by reducing oxidative stress.
* **Biosynthesis:** NADPH provides reducing power for various biosynthetic reactions, including fatty acid synthesis, cholesterol synthesis, and steroid hormone synthesis.
* **Detoxification:** NADPH is essential for detoxification pathways by reducing reactive oxygen species (ROS) and maintaining a healthy cellular environment.
* **Nucleotide Synthesis:** Ribose-5-phosphate, produced by the oxidative branch, is a precursor for the synthesis of nucleotides, which are essential components of DNA and RNA.
The pentose phosphate pathway is a flexible metabolic route that plays a pivotal role in cellular metabolism. It highlights the interconnectedness of different metabolic pathways and demonstrates the importance of NADPH in maintaining cellular function and homeostasis.'
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Proteins (3)
| Protein | Definition | Taxonomy |
|---|---|---|
| 6-phosphogluconate dehydrogenase, decarboxylating | A 6-phosphogluconate dehydrogenase, decarboxylating that is encoded in the genome of human. [PRO:DNx, UniProtKB:P52209] | Homo sapiens (human) |
| Glucose-6-phosphate 1-dehydrogenase | A glucose-6-phosphate 1-dehydrogenase that is encoded in the genome of human. [PRO:DNx, UniProtKB:P11413] | Homo sapiens (human) |
| GDH/6PGL endoplasmic bifunctional protein | A GDH/6PGL endoplasmic bifunctional protein that is encoded in the genome of human. [PRO:DNx, UniProtKB:O95479] | Homo sapiens (human) |
Compounds (34)
| Compound | Definition | Classes | Roles |
|---|---|---|---|
| furosemide | furosemide : A chlorobenzoic acid that is 4-chlorobenzoic acid substituted by a (furan-2-ylmethyl)amino and a sulfamoyl group at position 2 and 5 respectively. It is a diuretic used in the treatment of congestive heart failure. Furosemide: A benzoic-sulfonamide-furan. It is a diuretic with fast onset and short duration that is used for EDEMA and chronic RENAL INSUFFICIENCY. | chlorobenzoic acid; furans; sulfonamide | environmental contaminant; loop diuretic; xenobiotic |
| ketotifen | ketotifen : An organic heterotricyclic compound that is 4,9-dihydro-10H-benzo[4,5]cyclohepta[1,2-b]thiophen-10-one which is substituted at position 4 by a 1-methylpiperidin-4-ylidene group. A blocker of histamine H1 receptors with a stabilising action on mast cells, it is used (usually as its hydrogen fumarate salt) for the treatment of asthma, where it may take several weeks to exert its full effect. Ketotifen: A cycloheptathiophene blocker of histamine H1 receptors and release of inflammatory mediators. It has been proposed for the treatment of asthma, rhinitis, skin allergies, and anaphylaxis. | cyclic ketone; olefinic compound; organic heterotricyclic compound; organosulfur heterocyclic compound; piperidines; tertiary amino compound | anti-asthmatic drug; H1-receptor antagonist |
| metoclopramide | metoclopramide : A member of the class of benzamides resulting from the formal condensation of 4-amino-5-chloro-2-methoxybenzoic acid with the primary amino group of N,N-diethylethane-1,2-diamine. Metoclopramide: A dopamine D2 antagonist that is used as an antiemetic. | benzamides; monochlorobenzenes; substituted aniline; tertiary amino compound | antiemetic; dopaminergic antagonist; environmental contaminant; gastrointestinal drug; xenobiotic |
| thymidine | pyrimidine 2'-deoxyribonucleoside | Escherichia coli metabolite; human metabolite; metabolite; mouse metabolite | |
| methylprednisolone acetate | methylprednisolone acetate : An acetate ester resulting from the formal condensation of the 21-hydroxy function of 6alpha-methylprednisolone compound with acetic acid. Methylprednisolone Acetate: Methylprednisolone derivative that is used as an anti-inflammatory agent for the treatment of ALLERGY and ALLERGIC RHINITIS; ASTHMA; and BURSITIS; and for the treatment of ADRENAL INSUFFICIENCY. | 11beta-hydroxy steroid; 17alpha-hydroxy steroid; 20-oxo steroid; 3-oxo-Delta(1),Delta(4)-steroid; acetate ester; glucocorticoid; steroid ester; tertiary alpha-hydroxy ketone | anti-inflammatory drug |
| androsterone | 17-oxo steroid; 3alpha-hydroxy steroid; androstanoid; C19-steroid | androgen; anticonvulsant; human blood serum metabolite; human metabolite; human urinary metabolite; mouse metabolite; pheromone | |
| dehydroepiandrosterone | dehydroepiandrosterone : An androstanoid that is androst-5-ene substituted by a beta-hydroxy group at position 3 and an oxo group at position 17. It is a naturally occurring steroid hormone produced by the adrenal glands. Dehydroepiandrosterone: A major C19 steroid produced by the ADRENAL CORTEX. It is also produced in small quantities in the TESTIS and the OVARY. Dehydroepiandrosterone (DHEA) can be converted to TESTOSTERONE; ANDROSTENEDIONE; ESTRADIOL; and ESTRONE. Most of DHEA is sulfated (DEHYDROEPIANDROSTERONE SULFATE) before secretion. | 17-oxo steroid; 3beta-hydroxy-Delta(5)-steroid; androstanoid | androgen; human metabolite; mouse metabolite |
| pregnenolone | 20-oxo steroid; 3beta-hydroxy-Delta(5)-steroid; C21-steroid | human metabolite; mouse metabolite | |
| epigallocatechin gallate | (-)-epigallocatechin 3-gallate : A gallate ester obtained by the formal condensation of gallic acid with the (3R)-hydroxy group of (-)-epigallocatechin. epigallocatechin gallate: a steroid 5alpha-reductase inhibitor and antimutagen in green tea (Camellia sinensis) | flavans; gallate ester; polyphenol | antineoplastic agent; antioxidant; apoptosis inducer; geroprotector; Hsp90 inhibitor; neuroprotective agent; plant metabolite |
| 16-bromoepiandrosterone | 16alpha-bromo-3beta-hydroxy-5alpha-androstan-17-one: a synthetic adrenal hormone that reduced the incidence of tuberculosis and other opportunistic infections in AIDS patients | ||
| epicatechin | (-)-epicatechin : A catechin with (2R,3R)-configuration. | catechin; polyphenol | antioxidant |
| gallocatechol | (-)-epigallocatechin : A flavan-3,3',4',5,5',7-hexol having (2R,3R)-configuration. | catechin; flavan-3,3',4',5,5',7-hexol | antioxidant; food component; plant metabolite |
| (-)-catechin | (-)-catechin : The (-)-enantiomer of catechin. | catechin | metabolite |
| brexanolone | brexanolone : A 3-hydroxy-5alpha-pregnan-20-one in which the hydroxy group at position 3 has alpha-configuration. It is a metabolite of the sex hormone progesterone and used for the treatment of postpartum depression in women. brexanolone: a mixture of allopregnanolone and sulfobutylether‐beta‐cyclodextrin for treatment of postpartum depression | 3-hydroxy-5alpha-pregnan-20-one | antidepressant; GABA modulator; human metabolite; intravenous anaesthetic; sedative |
| tetrahydrodeoxycorticosterone | tetrahydrodeoxycorticosterone: RN given refers to (3alpha,5beta)-isomer | 21-hydroxy steroid | |
| 16-hydroxydehydroepiandrosterone | 16-hydroxydehydroepiandrosterone: RN refers to (3beta,16alpha)-isomer | 16alpha-hydroxy steroid; 17-oxo steroid; 3beta-hydroxy-Delta(5)-steroid; androstanoid; secondary alpha-hydroxy ketone | human metabolite; mouse metabolite |
| epicatechin gallate | (-)-epicatechin-3-O-gallate : A gallate ester obtained by formal condensation of the carboxy group of gallic acid with the (3R)-hydroxy group of epicatechin. A natural product found in Parapiptadenia rigida. epicatechin gallate: a steroid 5alpha-reductase inhibitor; RN given refers to the (cis)-isomer; structure given in first source; isolated from green tea | catechin; gallate ester; polyphenol | EC 3.2.1.1 (alpha-amylase) inhibitor; EC 3.2.1.20 (alpha-glucosidase) inhibitor; metabolite |
| methotrexate | dicarboxylic acid; monocarboxylic acid amide; pteridines | abortifacient; antimetabolite; antineoplastic agent; antirheumatic drug; dermatologic drug; DNA synthesis inhibitor; EC 1.5.1.3 (dihydrofolate reductase) inhibitor; immunosuppressive agent | |
| (-)-gallocatechin gallate | (-)-gallocatechin gallate : A gallate ester obtained by formal condensation of the carboxy group of gallic acid with the (3R)-hydroxy group of (-)-gallocatechin. A natural product found in found in green tea. | catechin; gallate ester; polyphenol | antineoplastic agent; EC 3.4.22.69 (SARS coronavirus main proteinase) inhibitor; human xenobiotic metabolite; plant metabolite |
| 21-hydroxypregnenolone | 21-hydroxypregnenolone : A hydroxypregnenolone that is pregnenolone which has been substituted by a hydroxy group at position 21. 21-hydroxypregnenolone: RN given refers to (3beta)-isomer; | 21-hydroxy steroid; hydroxypregnenolone; primary alpha-hydroxy ketone | mouse metabolite |
| epiandrosterone | epiandrosterone : A 3beta-hydroxy steroid that is (5alpha)-androstane substituted by a beta-hydroxy group at position 3 and an oxo group at position 17. | 17-oxo steroid; 3beta-hydroxy steroid; androstanoid | androgen; human metabolite |
| 4-phospho-d-erythronohydroxamic acid | |||
| 4-phosphoerythronate | 4-phospho-D-erythronic acid : The D-enantiomer of 4-phosphoerythronic acid. 4-phosphoerythronate: inhibits ribose-5-phosphate isomerase | 4-phosphoerythronic acid | Escherichia coli metabolite; mouse metabolite |
| paricalcitol | hydroxy seco-steroid; seco-cholestane | antiparathyroid drug | |
| polydatin | trans-piceid : A stilbenoid that is trans-resveratrol substituted at position 3 by a beta-D-glucosyl residue. | beta-D-glucoside; monosaccharide derivative; polyphenol; stilbenoid | anti-arrhythmia drug; antioxidant; geroprotector; hepatoprotective agent; metabolite; nephroprotective agent; potassium channel modulator |
| wedelolactone | wedelolactone : A member of the class of coumestans that is coumestan with hydroxy substituents as positions 1, 8 and 9 and a methoxy substituent at position 3. wedelolactone: antihepatotoxic coumestan from Eclipta prostrata and Wedelia calendulacea (both Asteraceae); structure given in first source | aromatic ether; coumestans; delta-lactone; polyphenol | antineoplastic agent; apoptosis inducer; EC 5.99.1.3 [DNA topoisomerase (ATP-hydrolysing)] inhibitor; hepatoprotective agent; metabolite |
| quercetin | |||
| (-)-catechin-3-O-gallate | (-)-catechin-3-O-gallate : A gallate ester obtained by formal condensation of the carboxy group of gallic acid with the (3R)-hydroxy group of (-)-catechin. | flavans; gallate ester; polyphenol | metabolite |
| indigo carmine | 3,5-di-O-(E)-caffeoylquinic acid: from roots of Lychnophora ericoides; structure in first source 3,5-di-O-caffeoyl quinic acid : A carboxylic ester that is the diester obtained by the condensation of the hydroxy groups at positions 3 and 5 of (-)-quinic acid with the carboxy group of trans-caffeic acid. Isolated from Brazilian propolis and Suaeda glauca, it exhibits hepatoprotective and cytotoxic activities. | ||
| thiocolchicoside | thiocolchicoside: used in combination with glafenine and meprobamate to tranquilize patients undergoing hysterosalpingography; structure | glycoside | |
| rucaparib | AG14447: Poly(ADP-ribose) polymerase inhibitor; structure in first source | azepinoindole; caprolactams; organofluorine compound; secondary amino compound | antineoplastic agent; EC 2.4.2.30 (NAD(+) ADP-ribosyltransferase) inhibitor |
| ml276 | |||
| mobic | meloxicam : A benzothiazine that is piroxicam in which the pyridin-2-yl group is replaced by a 5-methyl-1,3-thiazol-2-yl group. A non-steroidal anti-inflammatory drug and selective inhibitor of COX-2, it is used particularly for the management of rheumatoid arthritis. Meloxicam: A benzothiazine and thiazole derivative that acts as a NSAID and cyclooxygenase-2 (COX-2) inhibitor. It is used in the treatment of RHEUMATOID ARTHRITIS; OSTEOARTHRITIS; and ANKYLOSING SPONDYLITIS. | 1,3-thiazoles; benzothiazine; monocarboxylic acid amide | analgesic; antirheumatic drug; cyclooxygenase 2 inhibitor; non-steroidal anti-inflammatory drug |
| olanzapine | olanzapine : A benzodiazepine that is 10H-thieno[2,3-b][1,5]benzodiazepine substituted by a methyl group at position 2 and a 4-methylpiperazin-1-yl group at position 4. Olanzapine: A benzodiazepine derivative that binds SEROTONIN RECEPTORS; MUSCARINIC RECEPTORS; HISTAMINE H1 RECEPTORS; ADRENERGIC ALPHA-1 RECEPTORS; and DOPAMINE RECEPTORS. It is an antipsychotic agent used in the treatment of SCHIZOPHRENIA; BIPOLAR DISORDER; and MAJOR DEPRESSIVE DISORDER; it may also reduce nausea and vomiting in patients undergoing chemotherapy. | benzodiazepine; N-arylpiperazine; N-methylpiperazine | antiemetic; dopaminergic antagonist; histamine antagonist; muscarinic antagonist; second generation antipsychotic; serotonergic antagonist; serotonin uptake inhibitor |